The invention concerns generally a fuel tank and more particularly a fuel tank for a motor vehicle.
One form of fuel tank, generally referred to as a saddle tank, is formed by at least first and second tank regions of relatively large cross-section which form respective communicating sub-volumes of the tank. Those tank regions are in communication with each other by way of a further tank region of smaller cross-section. When considered in the position of installation of the tank, the tank region of smaller cross-section is formed by the bottom of the tank being displaced upwardly, whereby the bottom of the tank in the area of the tank region of smaller cross-section forms an inverted generally U-shaped configuration, whence the name saddle tank. The tank has at least one fuel delivery unit in the first tank region, and it also has means for venting the tank. There is at least one compensating or equalising line which intercommunicates the first and second tank regions on the basis of the principle of communicating tubes. The compensating line also has means for venting thereof.
By virtue of their saddle configuration such tanks are used primarily in relation to rear wheel drive motor vehicles where the tanks can be appropriately arranged over drive components, for example a universally joined shaft, or over parts of the exhaust system of the vehicle. For that purpose, in the region of the bottom, as indicated above the fuel tank has a recess extending upwardly into the tank which generally subdivides the tank into first and second tank regions of relatively large cross-section, constituting thus first and second tank chambers. For structural reasons and also for reasons which are relevant in terms of safety, those tank chambers do not have any communicating lines forming a communication therebetween, at a low level relative to the tank. In general, one of the first and second tank regions of relatively large cross-section accommodates the fuel delivery unit which comprises an electric fuel pump arranged in a reservoir which is also referred to as a surge pot or swirl pot. The reservoir ensures that the fuel pump is always supplied with fuel in all possible travel conditions and attitudes of the motor vehicle. As therefore fuel is conveyed to the engine only from a part of the fuel tank, namely the first tank region in which the fuel delivery unit is disposed, it is necessary to ensure that the fuel in the other regions of the fuel tank are also appropriately fed to the fuel pump. In general that is implemented by means of one or more suction jet pumps which are driven by way of a partial flow of fuel which is branched off the delivery flow of fuel to the engine or by a fuel return flow from the engine. Such suction jet pumps in which a jet of fuel, also referred to as the drive jet, in a branching from a fuel line produces a delivery suction action, are known units and can be found for example in DE 39 40 060 C2 to which reference may be made for a more detailed description of such a pump and the disclosure of which is thereby incorporated into this specification. In that way, by means of one or more suction jet pumps, fuel at other levels or in other sub-volumes of the fuel tank is continuously fed to the reservoir of the fuel delivery unit so that in terms of emptying the fuel tank it is possible to ensure that no unused fuel remains in parts of the fuel tank.
When the vehicle in which the tank is fitted is an inclined position or in different conditions of acceleration, particularly when the vehicle is subjected to transverse acceleration forces in bends, the design configuration of such a saddle tank in which the upwardly extending recess configuration in the bottom of the tank forms the saddle-shaped raised configuration in the interior of the tank means that it is quite possible for fuel to flow over from one tank chamber into the other, thereby resulting in different filling levels in the tank chambers. Such differences in level are generally not critical in regard to an adequate supply of fuel to the fuel pump in operation of the motor vehicle, but nonetheless it would still be desirable if the level of fuel in that region of the tank in which the fuel pump is disposed were higher than in the second tank region which is generally in opposite relationship to the first tank region transversely with respect to the longitudinal axis of the vehicle in which the tank is fitted.
It will further be noted that differences in level between the first and second tank regions of the tank, that is to say the two tank chambers defined thereby, can give rise to problems when refuelling the motor vehicle, particularly when the fuel in one chamber of the tank reaches a level at which a refuelling vent valve provided therein responds, although the maximum filling level has not yet been reached in the respective other chamber of the tank. In that case, the automatic shut-off valve in the refuelling gun shuts off prematurely in the refuelling procedure, with the consequence that the tank cannot be completely filled. That problem can occur in particular if the saddle configuration provided in the tank between the first and second tank regions is particularly pronounced and the refuelling vent valve shut-off level in at least one tank chamber is below the level of the top surface of the saddle configuration, so that equalisation of the levels in the chambers by virtue of fuel flowing across from one chamber into the other could occur only after the refuelling vent valve has responded.
It would be possible to avoid that by the provision of a refuelling vent valve in each chamber of the tank, so that the automatic shut-off valve in the refuelling gun will shut off only when both refuelling vent valves in the tank respond. That however involves the disadvantage that, in a situation in which the first refuelling vent valve to respond in a refuelling procedure is that which is disposed in the chamber into which the filler pipe of the tank does not open, there is the possibility of the tank chamber in question being overfilled so that the tank no longer has a sufficient expansion volume therein for possible expansion of the fuel. The other situation in which the refuelling vent valve in the chamber with the tank filling pipe responds first is not critical for the fuel can flow across from that chamber into the other chamber. It will be seen therefore that, with such a tank design configuration, it is not always possible to guarantee that the shut-off valve in the refuelling gun shuts off at the same filling level in the tank chambers.
For the purposes of equalising the filling levels in various chambers in a tank system, for example EP 0 228 167 involves a system wherein various chambers of a tank are in communication with each other by way of a compensating line or conduit, based on the principle of communicating vessels. It will be noted however that this involves ensuring the same filling level in the different volumes of the tank, both when the vehicle is stationary and also when it is in operation, although, as indicated above, that may not always be desirable.
A comparable arrangement for the purposes of equalising the levels of fuel in different volumes of a tank is to be found in DE 44 00 919 A1 describing a saddle tank of the general configuration referred to hereinbefore. In this case, the levels of fuel in the two chambers of the saddle tank are also equalised by means of a compensating line which is in the form of a siphon. The compensating line is communicated by way of a branch therefrom to a vacuum chamber of a suction jet pump which is operated by the return flow of fuel from the engine back to the tank. That arrangement ensures that any air or gas which has accumulated in the compensating line can be removed therefrom so that equalisation of the levels of fuel in the tank chambers can take place irrespective of fuel being removed by suction from the compensating line, which can happen in that situation.
That design is disadvantageous however insofar as an identical level of fuel in each of the tank chambers is guaranteed only if the vehicle is not transversely inclined. If the vehicle is transversely inclined when the tank is being refilled it is still not possible to ensure that the automatic shut-off valve in the refuelling gun shuts off when the level of fuel in the chambers is the same. In addition such a design configuration not only suffers from disadvantages in terms of refuelling, but moreover when the vehicle is stopped in a transversely inclined position and in particular when there is a low level of fuel in the tank, there is also the risk that the fuel can run from that chamber in which the fuel pump is disposed into the respective other chamber so that under some circumstances the fuel pump may no longer be adequately supplied with fuel.
An object of the present invention is to design a fuel tank in such a way that premature shut-down of the refuelling procedure and also overfilling of a tank chamber can be reliably avoided, using comparatively simple structural means.
Another object of the present invention is to provide a saddle-type fuel tank so designed as to ensure adequate filling of a tank chamber which accommodates a fuel pump.
Still another object of the invention is to provide a saddle fuel tank so designed as to ensure a certain minimum filling level of fuel in a first chamber thereof while on the other hand ensuring that a refuelling gun shuts off in a refuelling procedure when the levels of fuel in the tank chambers are at least approximately equal.
In accordance with the principles of the present invention the foregoing and other objects are attained by a fuel tank for a motor vehicle comprising at least first and second tank regions of relatively large cross-section, which form respective communicating sub-volumes or chambers of the tank. The first and second tank regions are in communication with each other by way of a further tank region of smaller cross-section. The tank region of smaller cross-section, in the position of installation of the tank, forms a constriction disposed in the upper part of the tank, between the first and second tank regions. At least one fuel delivery unit is disposed in the first tank region, and means for venting the tank are in the form of only a single common refuelling vent valve for the first and second regions of the tank, being arranged in the second tank region. At least one compensating line interconnects the first and second tank regions on the basis of the principle of communicating tubes. The compensating line is such that compensation or equalisation of the filling levels of the intercommunicating first and second tank regions is possible at least with a low filling level only in the event of such a drop in level at which the filling level in the first tank region is less than in the other regions of the tank.
As will be seen from a description hereinafter of a preferred embodiment of a fuel tank in accordance with the principles of the present invention, the tank configuration according to the invention ensures that, particularly when the engine of the motor vehicle in which the tank is fitted is stopped, equalisation of the levels of fuel as between the first and second tank regions of larger cross-section, which can also be referred to hereinafter for the sake of simplicity merely as the chambers, can take place in such a way that fuel can flow from the second chamber into the first chamber, but no fuel can flow back from the first chamber into the second chamber at least when the level of fuel falls below a given level. That has the advantage on the one hand that a certain minimum level of fuel in the first chamber is always guaranteed, and on the other hand the refuelling gun shuts off in a refuelling procedure when the level of fuel in the chambers is at least approximately the same.
It will be apparent that the problems involved with a saddle tank arise particularly when the tank is of an especially pronounced saddle configuration with the bottom of the tank constituting a large upwardly incursion into the volume of the tank to define respective chambers on each side thereof, in which case the tank region of smaller cross-section forming the communication between the chambers is of a particularly small volume so that equalisation of level of the fuel in the two chambers, by virtue of flowing across from one chamber into another, can only take place at a comparatively late stage and possibly after the refuelling vent valve has already responded.
In a particularly preferred feature of the tank according to the invention the compensating line has a first end opening into the first tank region at a higher level than in the second tank region. That affords a fuel backflow blocking effect from the first chamber into the second chamber only when the fuel falls below a given level.
Alternatively, in another preferred feature of the invention, a non-return valve or check valve can be provided in the first end of the compensating line. In that case the compensating line can be taken in both chambers approximately as far as the bottom thereof.
In the structure where the first end of the compensating line opens into the first tank region at a higher level than in the second tank region, it is desirable for the first end of the compensating line to open into an overflow container which accommodates that end of the compensating line. In that case, in the event of movements of the vehicle causing fuel surge or also when the vehicle is subjected to acceleration forces in the transverse and/or longitudinal directions, this configuration ensures that the first end of the compensating line remains immersed in fuel so that no air is drawn into the compensating line.
In a further preferred feature the compensating line can be connected by way of a branch connection to a reduced-pressure line, preferably at the highest location on the compensating line when considering the position of installation of the fuel tank, so that gases which possibly accumulate in the compensating line can be withdrawn therefrom. In that respect, the amount of fuel conveyed therein is to be comparatively small, and the cross-section of the compensating line can be so selected that it operates as a siphon, even when no reduced pressure is operative, for example when the engine is stopped.
In a preferred feature of this arrangement the reduced-pressure line can be connected for example to a pump which is operated by way of a partial flow of fuel which is branched from the fuel delivery flow produced by the fuel delivery unit or from a return flow of fuel from the engine back to the tank.
As an alternative it is possible to use an electric pump for venting the compensating line. That electric pump can be a separate electric pump. Alternatively for example venting of the compensating line can be effected by way of a second pump stage of the fuel delivery pump of the fuel delivery unit. That configuration is less preferred than the use of a separate electric pump however as using a second pump stage in that way has a lower level of efficiency in terms of conveying gas.
In a further preferred feature at least one check valve may be provided in the reduced-pressure line so as to ensure that the compensating line does not empty when the engine is stopped.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of a preferred embodiment.